First-principles approach to the understanding of π-conjugated organic semiconductors

We show how ab initio calculations based on density functional theory contribute to the understanding of the electronic and optical properties of organic semiconducting materials, which form the active layers in many opto-electronic applications. As a textbook example, we present the electronic structure and the optical properties of the oligo-phenylenes as evolving from their benzene-constituents. Thereby we discuss the dependence on the molecular length and introduce the modifications in the opto-electronic properties due to intermolecular interactions which are inherently present in the bulk phase.     

Synthesis and anticancer activity of new azo compounds containing extended π-conjugated systems

A series of novel azo compounds with extended π-conjugated systems were prepared by azo coupling reaction compounds trans-2-(4′-aminostyryl)-thiophene, 1-(4-aminophenyl)-4-phenyl-1,3-butadiene and 4-amino-4′-methoxystilbene with some phenols. The compounds were evaluated for their cytotoxicity against breast cancer adenocarcinoma (MCF-7), cervix adenocarcinoma (HeLa) and human embryonic kidney (HEK 293) cell lines using the MTT assay. The results showed all derivatives had more toxic effects than tamoxifen. Of all the compounds tested, the azo product obtained from coupling trans-2-(4′-Aminostyryl)-thiophene with 2-naphthol (compound 5b) exhibited the potent in vitro antiproliferative activity with IC₅₀ 27 ± 1 and 18 ± 0 µg/mL against MCF-7 and HeLa cell lines, respectively, while it was devoid of any cytotoxicity against normal HEK 293 cells even at 200 µg/mL.     

Correlation of π-conjugated oligomer structure with film morphology and organic solar cell performance

The novel methyl-substituted dicyanovinyl-capped quinquethiophenes 1-3 led to highly efficient organic solar cells with power conversion efficiencies of 4.8-6.9%. X-ray analysis of single crystals and evaporated neat and blend films gave insights into the packing and morphological behavior of the novel compounds that rationalized their improved photovoltaic performance.     

Reviewing extrapolation procedures of the electronic properties on the π-conjugated polymer limit

In this article, the extrapolation procedures of π-π* electronic transition energy on π-conjugated oligomers are reexamined. Different models, including the simplest coupled oscillator, the free electron, the Hückel approach, the molecular exciton model, and some specific fitting-functions, are compared using the transition energies derived from theoretical calculations on three thiophene-based oligomer series. Specifically, oligomers of up to 30 repeating units have been considered to include the saturation effects as a function of chain length. The coupled oscillator model of W. Kuhn and the fitting-function of Hirayama are the models that present the better suit on the transition energy interpolation as a function of chain length. Using only the first four oligomers of the series (n = 2 up to 8) yields an estimation of the transition energy on the polymer limit with an average error of ～1.5%. The vertical and adiabatic ionization potential present a better fit with the Hückel model approach. Finally, implications of the environmental polarity on the electronic properties, molecular geometry, charge distribution, and aromaticity are shortly discussed.     

Electrochemical functionalization of organic compounds by “small” molecules

The author's results and published data on the electrochemical insertion of small molecules (CO₂, SO₂, CS₂, NO) into organic substrates are reviewed. Special attention is paid to the cathodic carboxylation of halogen-containing aliphatic and aromatic compounds, polymers, and olefins, the sulfonylation and dithiocarboxylation of Freons, and anodic nitrosation of amines. The probable mechanisms of such processes and the effects of the nature of the reagents and the electrolysis conditions on the composition and yields of the final reaction products are examined.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 28, No. 2, pp. 97–114, March–April, 1992.     

Further evidences of the quality of double-hybrid energy functionals for π-conjugated systems

Despite numerous interesting efforts along decades to improve the accuracy of density functionals with broad applicability, such as B3LYP, there are still large sets of molecular systems where improvements are badly needed. We select π-conjugated systems as an example of the latter due to the subtle interplay between some physical effects affecting possibly most of the calculations: self-interaction or delocalization error, medium-range correlation signatures, dispersive-like weak interactions, and static correlation effects. We further assess a recently proposed modification of the B2-PLYP double-hybrid functional, called B2π-PLYP, that is expected to yield substantial progress for this kind of systems. Generally speaking, when compared with other more popular and older density functionals, double hybrids behave particularly accurate for π-conjugated systems without suffering the large errors that are common in former yet conventional methods.     

Review of the quantitative structure–activity relationship modelling methods on estimation of formation constants of macrocyclic compounds with different guest molecules

There is an increasing interest in the use of quantitative structure–activity relationship (QSAR) approaches as a progressive tool in modelling and prediction of many physicochemical properties in host–guest interactions of macrocyclic complexes. A review is presented on the QSAR modelling of macrocyclic compounds formation constants, which focus on two most interesting macrocycles, e.g. crown ethers and cyclodextrins (CDs), with different guest molecules. The review starts with a short overview on experimental methods of stability constant measurement, followed by a short explanation of the QSAR methodologies. In the next section, we focus on and discuss QSAR techniques that used to predict the stability (binding) constants or free energy complexation of some most interesting macrocyclic compounds, e.g. CDs and crown ethers, with different guest molecules including anionic, cationic and neutral molecules.     

Study of the aggregation behavior of a π-conjugated dendrimer with a twisted core

A dendrimer having phenylene vinylene and phenylene ethynylene moieties, a twisted core, and eighteen chiral centers on the periphery has been prepared in high yield by using Sonogashira and Horner–Wadsworth–Emmons reactions. UV–visible and fluorescence spectra and circular dichroism measurements have been envisaged to study the aggregation behavior.     

Solid-phase Pd-catalysed cross-coupling methods for the construction of π-conjugated peptide nanomaterials

We describe the development of two procedures for the synthesis of peptides that are embedded with a variety of π-conjugated semi-conducting oligomers. These procedures utilise solid-phase variants of classical palladium-catalysed cross-couplings commonly used to prepare π-conjugated oligomers. The resulting peptide–π–electron hybrids are soluble in aqueous media and self-assemble to produce 1D nanostructures, simultaneously forming networks of π-stacked conduits. The procedures have allowed for the inclusion of complex chromophores including mixed aryl units, ethynylene linkers and sexithiophenes where the latter peptide's nanostructures demonstrated substantial conductivity when employed as an active layer in a field-effect transistor.     

Electron correlation effects on the first hyperpolarizability of push-pull π-conjugated systems

The first hyperpolarizability (β) of representative push-pull π-conjugated compounds has been calculated at several levels of approximation to assess the effects of electron correlation. First, the 6-31+G(d) basis set has been shown to give the best balance between accuracy and computational resources for a polyene linker whereas for polyyne linker, the 6-31G(d) basis set is already an optimal choice. As a result of cancellations between higher order contributions, the MP2 method turns out to be the method of choice to predict β of push-pull π-conjugated systems since it closely reproduces the values obtained with the reference CCSD(T) scheme. Moreover, the SDQ-MP4 and CCSD approaches provide rarely improved estimates over MP2 while the MP4 method does not represent an improvement over MP4-SDQ or the SCS-MP2 method, over MP2. Among density functional theory exchange-correlation functionals, LC-BLYP is reliable when characterizing the changes of first hyperpolarizability upon enlarging the π-conjugated linker or upon changing the polyyne linker into a polyene segment. Nevertheless, its reliability is very similar to what can be achieved with the Hartree-Fock method and the MP2 scheme is by far more accurate. On the other hand, the BLYP, B3LYP, and BHandHLYP functionals perform quantitatively better in a number of cases but the trends are poorly described. This is also the case of the B2-PLYP and mPW2-PLYP functionals, which are often the most accurate, though they underestimate the increase of β when going from polyyne to polyene linkers and overestimate the enhancement of β with chain length.     

Effect of structural and thermodynamic factors on the sorption of hydrogen by metal–organic framework compounds

The characteristics of the sorption of hydrogen by metal–organic framework compounds (MOF) were examined, and the structural and thermodynamic factors that favor the sorption of H₂ by such substances were determined. The effect of the structure of the MOF and the size and geometry of the pores on the sorption characteristics was analyzed. Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 45, No. 2, pp. 67-87, March-April, 2009.     

Reactions of π-allyltricarbonyliron halides and the synthesis of new organoiron compounds

The reactions of [π-C₃H₅Fe(CO)₃X] [where X = Cl (1, Br (2) or I (3)] with different chemical species are described. Thus, 2, and 3 react with Ph₂CNLi in Et₂O to yield [(π-C₃H₅)(CO)₃Fe(NCPh₂)], while the reaction of 1 with PhC(S)N(Me)Li in THF yielded a novel σ-allylironcarbonyl compound. Ethynyl magnesium bromide, HCCMgBr, reacts with 3 in THF to give a π-allyltricarbonyl ethynyliron complex, which undergoes a dipolar cycloaddition reaction with PhCNO in Et₂O, yielding a novel organoiron complex, [(μ-CO)bis{5(σ-allyltricarbonyliron)(3-phenylisoxazole)}]. The reaction of [(π-C₃H₅(CO)₃FeNa] with ClCH₂CH₂NMe₂ is also described. Data on molar conductances, molecular weights, and IR and ¹H NMR spectra, were used to assign structures.     

Anion modules: building blocks of supramolecular assemblies by combination with π-conjugated anion receptors

Dipyrrolyldiketone boron complexes, as π-conjugated acyclic anion receptors, act as building subunits of various assemblies through noncovalent interactions in the form of receptor-anion complexes. Instead of, or in addition to, the modification of receptor structures, the introduction of anion modules as building blocks for the assemblies was found to be useful in forming various soft materials. Gallic carboxylate derivatives 3-n (n = 16, 18, 20), as tetrabutylammonium (TBA) salts, form receptor-anion-module complexes that can be used to fabricate supramolecular assemblies. Combinations of aliphatic anion modules 3-n and receptors 1a,b along with a TBA cation afforded products with mesophases, which were indicated by differential scanning calorimetry and polarized optical microscopy. X-ray diffraction measurements of the solid states and mesophases of 1a·3-n·TBA and 1b·3-n·TBA revealed highly ordered structures including lamellar structures, which could be modulated by the lengths of the alkyl chains of the modules. Functional materials exhibiting electrical conductivity were fabricated by using combinations of anionic building blocks that form assemblies by themselves and π-conjugated acyclic receptors.     

Simultaneous determination of phenolic compounds by means of an automated voltammetric “electronic tongue”

Zirconium(IV) selenoiodates have been synthesized under a variety of conditions. The most chemically and thermally stable sample is prepared by adding a mixture of aqueous solutions of 0.1 mol L^–1 potassium iodate and 0.1 mol L^–1 sodium selenite to aqueous solution of 0.1 mol L^–1 zirconium(IV) oxychloride. Its ion-exchange capacity for K⁺ and Pb²⁺ was found to be 3.20 and 2.35 meq g^–1 dry exchanger, respectively. The material has been characterized on the basis of chemical composition, pH titration, and thermogravimetric analysis. The effect on the exchange capacity of drying the exchanger at different temperatures has also been studied. The analytical importance of the material has been established by quantitative separation of Pb²⁺ from other metal ions.     

The role of the Baeyer–Villiger reaction in the liquid-phase oxidation of organic compounds

The data on the composition of ester products formed in the Baeyer–Villiger reaction in the liquid-phase oxidation of organic compounds with molecular oxygen, on production channel of peroxy acids, as well as on the influence of a carbonyl compound structure on its reactivity in reactions with peroxy acids have been classified and considered. The Baeyer–Villiger reaction was shown to be the main source of accessory primary alcohol esters and lactones in industrial processes of aerobic oxidation of cyclohexane and paraffin hydrocarbons.     

Determination of boron in organic compounds by microwave plasma–atomic emission spectrometry

We propose a method for the determination of boron in aliphatic and aromatic trifluoroborates (including perfluorinated ones), ethers, and organoboron compounds containing dioxoborolane fragments, pyridine, and pyrazole rings, and triple bonds. The substances were decomposed by the oxygen flask combustion method. Boron was determined on an Agilent 4100 microwave plasma–atomic emission spectrometer. A number of organic compounds were analyzed, and the mass fraction of boron was determined with an error less than ±0.3 abs. %.     

Determination of volatile organic compounds by solid-phase microextraction—gas chromatography-differential mobility spectrometry

Up to now the analysis of aqueous samples by ion mobility spectrometry is a challenge due to the lack of suitable sample introduction systems. But just the introduction of asymmetric field strengths leading to a higher selectivity and sensitivity, this technique is of growing interest for on-site analysis of contaminated water. In this work, first results for the preparation of a portable GC-DMS system are presented. A differential mobility spectrometer (DMS) with a ⁶³Ni ionization source has been used as a detector for the gaschromatographic separation of benzene, toluene, ethylbenzene m-, o-, and p-xylene (BTEX) in water. Separation from the matrix and pre-concentration of the analytes was achieved by solid-phase microextraction (SPME). The influence of the different chromatographic parameters, extraction conditions and differential mobility spectrometry settings on the sensitivity and signal shape were investigated. Results of the optimization of the analytical method as well as analytical validation parameters such as method detection limit, limit of quantification and the repeatability are discussed. Additionally, the applicability of the method was demonstrated by the analysis of a real surface water sample.     

Adsorption of volatile organic compounds on Carbopack Y adsorbent modified by β-cyclodextrins

The thermodynamic study on the adsorption of vapor-phase organic compounds on surface of the Carbopack Y carbon-based sorbent modified by monolayer of heptakis(2,3,6-tri-O-methyl)-β-cyclodextrin or heptakis(2,3,6-tri-O-acetyl)-β-cyclodextrin was performed. The dependence of the thermodynamics of absorption on the structure of the adsorbate and modifier molecules was studied.     

Atropselective alkylation of biaryl compounds by means of transition metal-catalyzed C–H/olefin coupling

The reaction of 2-(1-naphthyl)-3-methylpyridine with olefins in the presence of [RhCl(coe)₂]₂ and PCy₃ as the catalyst resulted in the alkylation of the naphthyl ring at the 2-position in good yield. The replacement of PCy₃ with the chiral ferrocenyl phosphine, (R),(S)-PPFOMe, as the ligand resulted in atropselective alkylation of the naphthylpyridine derivatives. Ethylene reacted with the biaryl compounds to give the corresponding addition products in moderate yields with fair to good ee's (up to 49% ee).     

Survey of recent advances of in the field of π-conjugated heterocyclic azomethines as materials with tuneable properties

This account gives an overview of our recent work in the area of conjugated azomethines derived from 2-aminothiophenes.It will be presented that mild reaction conditions can be used to selectively prepare symmetric and unsymmetric conjugated azomethines.It further will be demonstrated that azomethines consisting of various 5-membered aryl heterocycles lead to chemically,reductively,hydrolytically,and oxidatively robust compounds.The optical and electrochemical properties of these materials can be tuned contingent on the degree of conjugation,type of aryl heterocycle,and by including various electronic groups.The end result is materials having colors spanning 250 nm across the visible spectrum.These colors further can be tuned via electrochemical or chemical doping.The resulting doped states have high color contrasts from their corresponding neutral states.The collective opto-electronic properties and the means to readily tune them,make thiophenoazomethine derivatives interesting materials for potential use in a gamut of applications.